This invention relates to a magnet assembly in the form of a magnet encapsulated within a non-metallic containment body and, more particularly, to an encapsulated magnet assembly constructed to eliminate heat induced magnetic losses that are known to occur during the process of making the magnet assembly.
Encapsulated magnet constructions known in the art comprise a magnet disposed within a non-metallic containment body. Encapsulated magnet constructions of this type can be used in magnetically-driven applications such as pumps and the like, where it is essential that the metal magnet remain isolated from the displaced or pressurized liquid. An example application for use of an encapsulated magnet construction is in centrifugal pumps, where the encapsulated magnet construction is connected to or is in the form of a pump impeller that is placed in contact with the process liquid. The encapsulated magnet/impeller is driven, i.e., rotated, by a rotating magnet that is isolated from the process liquid. The encapsulated magnet is configured such that one of its magnetic poles are uniformly oriented toward the opposite poles of the rotating magnet. In this manner, a magnetic force or field is developed between the magnets that locks or couples the magnets together so that the encapsulated magnet impeller rotates around the rotating magnet, causing the encapsulated magnet to pressurize the process fluid.
Encapsulated magnet assemblies known in the art are typically formed by inserting a magnet into a non-metallic magnet containment body and then fusion welding a non-metallic cap to the body to encapsulate the magnet therein. Other known encapsulated magnet constructions are formed by in-situ encapsulation, whereby the metallic magnet body is surrounded by a non-metallic material by injection mold process. The in-situ encapsulation process enables magnet encapsulation in a single step without having to perform a multi-step encapsulation operation of inserting the magnet into a containment body and then welding a cap to the containment body to achieve encapsulation.
A common feature of each of the above-described encapsulated magnet constructions is that they are formed by subjecting the magnet to heat, either during the step of welding the cap to the containment body or during in-situ encapsulation by injection molding. Encapsulated magnet constructions formed in this manner are known to suffer magnetic field losses during the fabrication process due to their unprotected exposure to this heat. Accordingly, encapsulated magnet constructions produced in this manner are known to display magnetic field losses that may render them unuseful, either initially or after a period of time, to perform as intended in a particular magnetically-driven application, e.g., to drive a magnetically-coupled pump or the like.
Additionally, while such known encapsulated magnet constructions do provide a structure that isolates or shields the metallic magnet component from the outside environment, be it gas or liquid, they fail to provide a structure that prevents the magnet from moving internally within the containment body, e.g., from becoming decoupled from and rotating within the containment body during operation within a given device. For this reason, such conventional encapsulated magnet constructions are known to have a reduced service life due to either an initial or eventual decoupling of the magnet from the containment body. When used in the application of a magnetically-coupled pump, such initial or eventual magnet decoupling, while not causing the magnet to become exposed to the process liquid, will reduce pump efficiency and the ability of the pump to produce a desired output pressure.
It is, therefore, desired that an encapsulated magnet assembly be constructed in such a manner as to reduce or eliminate magnetic losses otherwise known to occur during the fabrication process, thereby providing an encapsulated magnet construction having magnetic properties that is approximately that of the preinstalled magnet itself. It is also desired that such encapsulated magnet assembly be constructed to prevent the magnet from becoming decoupled from the containment body, to thereby ensure a long and predictable service life when used in magnetically-driven applications.
The present invention comprises an encapsulated magnet assembly and method of making the same that minimizes or eliminates altogether thermally-induced magnetic field losses known to occur in conventional encapsulated magnet assembly devices, and that also prevents the magnet from becoming decoupled from its encapsulating housing during use. Encapsulated magnet assemblies of this invention comprise a magnet containment housing that is formed from a non-metallic material having an magnet chamber disposed therein for accommodating a magnet. A magnet is disposed within the magnet chamber and an end cap formed from a non-metallic material is attached to an end of the housing to sealably encapsulate the magnet therein. A thermally-insulating spacer is interposed between the magnet and the cap before attachment of the cap to the housing, and serves to minimize or prevent altogether unwanted transfer of thermal energy to the magnet during the process of sealing the end cap to the housing. The housing additionally includes means for maintaining the rotational position of the magnet within the housing magnet chamber fixed during operation of the encapsulated magnet assembly in a device such as a centrifugal pump